Electrical wires are most often made with copper or aluminum conductors. These may be of one solid piece, or stranded. For ease of connections, for instance to grounding studs, or power strips, a lug or terminal is often attached to the end of the wire. The terms lug, terminal lug, and terminal will be used interchangeably in this application. A wire with a terminal, will be termed a “cable” in this application. The cable, including the interface between the terminal and the conductor, must efficiently conduct the electricity that the cable is meant to carry. If the conductance at the interface is not efficient (if resistance is high), the cable may not perform the function for which it is intended, or it may overheat. Usually, the terminal mechanically fastens to the aluminum or copper conductor. If there is insulation on the wire, it is first removed or penetrated in an area sufficient to allow proper electrical contact which is usually metal-to-metal contact. Sometimes attachment occurs with a heat process such as welding or soldering, however these tend to be slower methods than mechanical fastening. Also, the heat of these processes could deteriorate the properties of the nearby insulation that is on the conductor. Mechanical crimping of a terminal around a wire is commonly used. However, the chemistry of aluminum oxidation makes crimping to an aluminum wire more difficult than to a copper wire, as will be explained.
It is known that aluminum resists corrosion (oxidation) better than steel does. For example, lawn furniture made of steel develops flaking rust (oxidation) but aluminum furniture does not. Aluminum also oxidizes almost instantaneously when exposed to air, but the oxide does not subsequently flake off. Instead, the oxidized surface layer is very thin and very strong. It protects the nonoxidized aluminum below by separating it from the surrounding air. This property of aluminum presents a problem in the manufacture of aluminum cables because the oxide layer is a poor conductor of electricity. Thus, one consideration in aluminum cable manufacture is how to get good electrical conductivity between a terminal and an aluminum wire. Preferably, good electrical conductivity is achieved in a cost effective manner that has a low opportunity for problems to arise during the manufacturing process.
Another consideration in cable manufacture is how to create a cable that resists moisture and air infiltration between the terminal and the conductor. In many cases this means making an airtight connection between the terminal and the exterior of the wire insulation.
Still another consideration in cable manufacture is how to provide a terminal/cable combination that has a consistent and strong geometry. Preferably the terminal and cable are straight and smooth to avoid stress concentrations. With stranded wire, severing one or more strands during the terminal attachment process should also be avoided.
There have been many attempts at making a terminal for use with Aluminum wire. For example, U.S. Pat. No. 3,955,044 to Hoffman et al., issued May 4, 1976 shows one such prior art. FIGS. 1-3 in the present application are representative of a prior art configuration showing some drawbacks to the prior art. A tin plated copper terminal 10 includes a ring tongue (RT) style connector portion 11, a cylindrical wire barrel 12, a perforated liner 14, and an annular ring 16 with an inclined wall 18. Terminal 10 is shown in exploded view with stranded aluminum wire 20 having conductor strands 22, an insulating sheath 24, and an abrasion sheath 26. FIGS. 2 and 3 show the wire 20 installed in the terminal 10, before and after crimping by die set 27. In FIG. 3, the deformation, known as terminal skew, of the terminal 10 is extensive, with the upper mounting surface 28 and lower mounting surface 30 no longer parallel to the axis 32 of the wire 20. Also, with such a design several conductor strands 22 might be severed as shown at 34 in the area of annular ring 16. The pre-crimp geometry of FIG. 2 is represented with phantom lines in FIG. 3. The extensive extrusion and crimping of the conductor strands 22 and barrel 12 changes the length 36 and the angle 38 an amount that is significant and not precisely predictable.
There are many drawbacks to the prior art, including, but not limited to the multiple pieces that are required and that lead to increased cost and opportunity for assembly errors, severing of one or more strands, and the non-linear alignment between the connector portion and the wire barrel after crimping. The present invention addresses these drawbacks and other drawbacks in the prior art.